One of the most common mass storage devices used with computers of all sizes is the so-called hard disk drive, taking its name from the rigid disk on which data is recorded as magnetic patterns in a thin layer of a magnetic recording medium on the disk surface. The data is recorded and read by a magnetic transducer or head carried by a flyer which is aerodynamically suspended above the rotating disk so as to maintain the tips of the transducer's magnetic core closely spaced to the magnetic coating surface. The transducer is often produced through a conventional thin film process. Because a preferred ceramic material frequently used for the flyer is somewhat conductive, it is necessary to start the transducer-forming process on this material with deposition of an insulating base layer, usually alumina, on its surface, which prevents shorting of the electical winding.
It has been discovered that electrostatic charges can build up on various of the elements of a transducer so mounted on a conductive flyer and separated from it by an insulating layer, see U.S. Pat. No. 4,317,149 (Elser). Elser describes one mechanism by which such charges can be created on the transducer. These charges arc arcoss the edge of the insulating layer between the pole tips and the flyer itself, and cause erosion of the pole tips. This is not desirable, because continued arcing will cause the pole tips to recede from the edge of the flying surface, resulting in degraded performance of the transducer in reading and writing the data. It is felt that charges on the core may be created at almost any time in the life of the transducer, so that arcing must be continuously avoided.
We believe an alternative condition also obtains, whereby a voltage potential may be induced in the leads from a neighboring electrostatic field after they are attached to the transducer winding. This induced voltage may cause the perforation of the insulating material surrounding the winding because of its relatively low breakdown voltage, or may cross the insulation capacitively from the winding to the core. Even though the potential induced in the leads may be only in the tens of volts, the voltage passes through the winding insulation by either of these mechanisms to the core and then arcs from the pole tips to the flyer. This is possible because the extreme thinness of the insulating layer separating the transducer pole tips from the flyer results in a relatively small breakdown voltage. The winding insulation may well be damaged if arcing between the winding and the core occurs, causing the performance of the transducer to be degraded and perhaps even completely destroyed. It is believed that once the leads are attached to the circuitry which produces the write signal and receives the read signals, the circuitry's input impedance is low enough to prevent these electrostatically-induced voltages from building up on the leads and causing damage.
Another problem less well known at the present time, is that arcing may dislodge particles which are of a size capable of causing a crash of the flyer, where the aerodynamic suspension fails and the flyer strikes the recording layer surface, dislodging more and then even more particles in an avalanche pattern. This is true even if the arcing occurs before the transducer is placed in service, since the debris dislodged may adhere to the flyer until it is placed in service.
The Elser patent deals with the electrostatic discharge problem by providing alternative, lower breakdown voltage arcing paths remote from the pole tips, so that the arcing can occur without causing damage to the pole tips. But this approach does not solve the problem caused by particles dislodged by arcing. Nor does it deal with the problem of voltage induced on the winding which causes internal arcing. We feel is is desirable to completely avoid arcing both externally and internally so as to reduce or eliminate the problems decribed.